Now stringent diesel emission regulations have had the effect of limiting the acceleration rates of turbodiesel powered vehicles. A need for supercharging of turbodiesel engines to improve their performance in the low RPM range has been recognized by most turbodiesel engine manufacturers and users. Positive displacement superchargers, such as well known Roots type and rotary type blowers driven directly by the engine via speed increasing gear trains have been utilized by major turbodiesel manufacturers. Fixed gear ratio mechanical superchargers suffer from four vary undesirable features which are:
1) supercharger speed cannot practically be controlled independently of engine speed, PA1 2) a fixed gear ratio mechanical supercharger proportions the engine intake air flow closely to the engine speed regardless of the engine load, thus the supercharger is not able to achieve the optimum air flow to fuel ratio at all engine loads, PA1 3) a mechanical clutch is required to disconnect the blower from the engine when not needed which result in an abrupt change in boost, and PA1 4) the positive displacement blower blocks the air flow through it when disconnected from the engine.
The applicant has been granted U.S. Pat. No. 5,421,310 issued on Jun. 6, 1995 for a hydraulic supercharging system utilizing a miniature, very high speed hydraulic turbine driving a compact centrifugal compressor to supercharge a turbocharged engine. The advantage of this system is its ability to modulate the supercharger speed independently of the engine speed and thus achieve substantially optimum boost and air/fuel ratio at all engine loads and speeds. It utilizes a "stand alone" relatively simple hydraulic system incorporating prior art bearings lubrication and seals functions. This hydraulic supercharging system does, however, require a substantial amount of engine mechanical power to drive the hydraulic system which may be undesirable is some applications. Applicant has also been granted U.S. Pat. No. 5,427,508 issued Jun. 27, 1995 for an electro-pneumatic blower and U.S. Pat. No. 5,346,364 issued on Sep. 13, 1994 and U.S. Pat. No. 5,471,965 issued on Jun. 27, 1995 disclosing high speed hydraulic turbines. The teachings of all the patents referred to in this paragraph are hereby incorporated herein by reference.
What is needed is an engine supercharging system which provide the advantages of the hydraulic system with a substantial reduction in the power required from the engine to drive the hydraulic system.